Remember that the variables a and b in the formula are the legs and c is the hypotenuse. So that means that 15 and x are the legs and 17 is the hypotenuse. Plug those numbers where they go in the formula like below:
15^2+x^2=17^2
Go ahead and square the 15 and 17 to simplify it a little.
225+x^2=289
Now, get the x by itself by subtracting 225 from each side
x^2=64
Take the square root of each side to remove the squared on x and solve.
